jaffacake - The whole thing about 'high' or 'middle' income is a piece of nonsense tbh.
So much depends on your outgoings, where you live, when you got into the housing market (if you own a house) etc etc
For example, a family who use relatives for free childcare may be massively better off than a family earning considerably more who have to pay a couple of grand a month on childcare. Or a low income family may be topped up by benefits, whereas a family with a higher income may miss out on any sort of benefits.
When I had two children in nursery, the nursery workers (who I suspect were on pretty low incomes) probably had more disposable income than I did. I am also pretty certain that at various points in my career, some of the part time lower paid staff in my school (eg office staff, teaching assistants) probably had as much, or more, disposable income. From friends working in these positions, I know that, for example, one woman who is a lone parent gets a big chunk of her rent paid, free prescriptions etc etc
So it's not really very helpful to talk in terms of 'middle income' as it often bears no relationship to what you actually have in your pocket at the end of the month!